28 TIMBER OF THE EDWARDS PLATEAU OF TEXAS. 



At the bottom of the gorge the timber growth still continues, almost 

 blocking the channel, which, instead of being swept clear by Hood 

 water, is filled with forest litter and fine mineral sediment. 



What happens in these two cases after a heavy rainfall ? In the south 

 gorge the water at once begins to pour down as from a steep roof, 

 converging into swift streamlets which erode every vestige of organic 

 soil, and in addition the adobe and smaller stones, which it often 

 piles in heaps below. Uniting at the main channel, these flood waters 

 pour down with the characteristics of a mountain torrent. In the 

 north gorge, on the contrary, the downpour, particularly during the 

 season when foliage is on (which is also the season of heaviest rains), 

 broken by the timber covering, is shorn of its force, and, instead of 

 packing the soil and debris and then running off, is largely taken up 

 by the porous ground. Thus the water is prevented from getting 

 head enough to form a flood or to erode the soil, and at the same time 

 is detained so that vastly greater quantities are absorbed by the lime- 

 stone formation beneath. 



In the case of some of the gorges farther up the river, e. g. , Devils 

 Gorge, the upper slopes are bare; but farther down there begins a 

 heav} r growth of mountain oak or mixed timber, which extends to the 

 bottom of the gorge. Beneath this is a rich soil, covered by a foot 

 or more of looser organic debris, which disorganizes slowly because 

 so persistently dried out, but which retains moisture beneath and is 

 all the more active in absorbing the rainfall. In spite of the velocity 

 gained by the water on the upper slopes, its progress is so checked 

 by the vegetation and debris below that only after an unusual down- 

 pour does the channel flood attain violence. 



It is unusual for any of these short gorges to maintain running 

 streams throughout the season. Ordinarily they are entirely dry 

 before midsummer. In those gorges whose slopes are denuded, the 

 flow ceases almost directly after each fall of rain. But there is one 

 gorge which furnishes a very instructive object lesson of a different 

 character. It is some 12 miles up the river from Austin, and is 

 heavily timbered. During the spring of 1903 this gorge became a 

 favorite resort because of its natural wooded beauty, and especially 

 because of its series of cascades and deep, clear pools. It had all the 

 appearance of a mountain stream of the humid Eastern States. The 

 streams which feed the streamlet appear to be gravity springs, from 

 which flows water which has fallen upon the local catchment area. 



Naturally, their flow reflects the season's rainfall. The upper 

 spring, at least, dries up with the advance of the dry season, and the 

 flow from the main lower one becomes very meager. Nevertheless, 

 these springs were still flowing freely long after the streams in all the 

 other gorges had been completely dr}^. This difference seems to be 

 due to the two facts that, in the first place, the local catchment area 



